I'm running FC 14 on an Alienware m15x-R1. It's an older one that they made before Dell bought them out.

My problem is that the internal speakers don't work, but if I plug a headset in to the audio jack, it works fine.

lspci tells me I have an audio device Intel Corp HD Audio Controller, which may or may not be helpful. I booted it up with an Ubuntu live CD just to make sure it was the hardware, and I get the same results.

Look at the settings in alsamixer -c0 for any muted outputs.
also in the Pulseaudio Volume Control (yum install pavucontrol if you don't have it) and check the correct output is selected and nothing is muted.